Provide getOrSet method for ThreadLocal<T: Any>

#KT-7927 Fixed

libraries/stdlib/src/kotlin/concurrent/Thread.kt

@@ -80,6 +80,22 @@ public fun thread(start: Boolean = true, daemon: Boolean = false, contextClassLo
     return thread
 }
 
+/**
+ * Gets the value in the current thread's copy of this
+ * thread-local variable or replaces the value with the result of calling
+ * [default] function in case if that value was `null`.
+ *
+ * If the variable has no value for the current thread,
+ * it is first initialized to the value returned
+ * by an invocation of the [ThreadLocal.initialValue] method.
+ * Then if it is still `null`, the provided [default] function is called and its result
+ * is stored for the current thread and then returned.
+ */
+public inline fun <T: Any> ThreadLocal<T>.getOrSet(default: () -> T): T {
+    // TODO: replace let with apply or touch
+    return get() ?: default().let { set(it); it }
+}
+
 /**
  * Allows you to use the executor as a function to
  * execute the given block on the [Executor].

libraries/stdlib/test/concurrent/ThreadTest.kt

@@ -28,4 +28,24 @@ class ThreadTest {
         assertEquals("Hello", future.get(2, SECONDS))
     }
 
+    test fun threadLocalGetOrSet() {
+        val v = ThreadLocal<String>()
+
+        assertEquals("v1", v.getOrSet { "v1" })
+        assertEquals("v1", v.get())
+        assertEquals("v1", v.getOrSet { "v2" })
+
+        v.set(null)
+        assertEquals("v2", v.getOrSet { "v2" })
+
+        v.set("v3")
+        assertEquals("v3", v.getOrSet { "v2" })
+
+
+        val w = object: ThreadLocal<String>() {
+            override fun initialValue() = "default"
+        }
+
+        assertEquals("default", w.getOrSet { "v1" })
+    }
 }